What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (36 page)

Why all the cautions about cooling a soup or stock quickly to prevent the growth of dangerous bacteria? After all, the stuff has just been simmered for more than an hour. Wouldn’t that have sterilized it, as long as I keep it covered while it cools so that new bacteria don’t drop in for dinner?

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U
nfortunately, no. Not all bacteria are killed at 212°F (100ºC). Some of them can survive by protecting themselves within virtually invulnerable coatings. They’re then called spores.

Most species of bacteria reproduce by binary fission, each organism splitting into two whole new organisms. That’s why they can grow at exponential rates. Once they get started, bacteria can increase their numbers from, say, 5,000 to 10,000 to 20,000 to 40,000, and so on, doubling as often as every ten minutes, until they can reach as many as 10 billion in every milliliter (one-thirtieth of an ounce) of your soup or stock by the time they run out of nutrients.

But when conditions are not conducive to their growth, or are even out-and-out hostile, some species of bacteria (and fungi) can ride it out as spores—dormant and virtually indestructible forms. Protected by tough, horny suits of armor, the spores are capable of surviving such calamitous surroundings as boiling water, nutritional deprivation, dryness, freezing, ultraviolet light, corrosive chemicals, and even heavy-metal rock music. When conditions improve, such as when your stock cools to a comfortable growth temperature, the spores can transform themselves into whole new individuals that will resume reproduction in the normal way.

A common pathogenic genus of spore-forming bacteria found in soil, water, and the intestinal tracts of humans and animals is
Clostridium,
especially the species
C. perfringens,
which is a major cause of food poisoning, and the much rarer
C. botulinum,
which produces botulin toxin, one of the most potent poisons known.
Clostridium
bacteria don’t need oxygen to live; in fact, they can’t survive in air, so the interior of a pot of stock is a perfect growth environment for them.

To kill spores, temperatures significantly higher than 212°F (100ºC) are needed. That’s why medical and surgical equipment is sterilized in an autoclave, a sort of pressure cooker. Under higher pressures, water boils at higher temperatures. Pressure cookers and autoclaves are closed containers in which the steam pressure from boiling water builds up enough to raise the boiling temperature to about 250°F (141°C), high enough to kill most bacterial spores.

I have traveled in quite a few countries in which my American stomach was unaccustomed, and therefore vulnerable, to the local . . . shall we say, wee little beasties that can be found in food. I stuck as much as possible to deep-fried foods (which are often the best local snacks anyway), because oil at 350°F (177°C) will kill almost anything.

The inside of a food can is an excellent oxygen-free breeding place for
Clostridium
spores. That’s why, after being filled and sealed, canned foods are sterilized by being heated in high-pressure steam kettles or cookers at temperatures of 240 to 250°F (116 to 141°C). If the sterilization isn’t complete and live bacteria grow in the can, they produce hydrogen gas, which can cause the can to bulge. So if the end (the weakest part) of a food can bulges or buckles even slightly when you press on it, use the can to practice your shot-put into the nearest landfill.

I learned at my mother’s knee to add a little acid—lemon juice, vinegar, or wine—to increase the amount of calcium that would come out of the bones when making a stock. Does it work?

....

Y
es, to a slight extent.

Bones are a combination of two kinds of substances: (1) soft, organic cells and proteins, which are partly extracted into the water during the simmering of a stock, and (2) a hard, inorganic mineral that doesn’t dissolve appreciably or contribute any flavor. This mineral material in both bones and teeth is primarily a calcium phosphate compound called hydroxyapatite, which, as your dentist will hasten to inform you, is attacked by acids. (In the case of tooth decay, the acids are produced by bacteria.)

Unless the acid is very strong, it will take a long time to dissolve very much of the calcium phosphate in your soup bones. The small amounts of relatively weak acids in lemon juice, vinegar, or wine won’t extract much calcium, even after hours of simmering.

But if you want to have some fun, try this: Immerse a cooked and well-cleaned chicken bone (the thigh bone works well) in a covered jar of undiluted vinegar and let it soak for four or five weeks. The vinegar’s acid will dissolve enough of the hard hydroxyapatite so that mostly the soft, organic materials remain. You will then be able to startle your friends by bending a very flexible chicken bone.

Tell them it came from a rubber chicken.

Is the following assertion true? “Cooking with wine adds extra flavor to a dish because the alcohol dissolves and releases flavor components that are not dissolvable in water.” I’ve seen this statement, or statements like it, in several places. But I’m a chemist, and it just doesn’t sound right to me.

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C
hefs I’ve spoken with accept this idea as quite reasonable, and indeed it does seem to make sense on the surface of it, because many substances do indeed dissolve in alcohol but not in water.

Nevertheless, the statement is false. The real reason we use wine in cooking is simply that a good wine contributes its flavor to the dish. It has nothing to do with dissolving flavor components.

Here’s the catch: In a mixture of alcohol and water, such as wine, the alcohol doesn’t act like pure alcohol and the water doesn’t act like pure water. They act like a mixture of alcohol and water, and a mixture can have quite different properties from either of the pure liquids.

For example, if we mix equal amounts of alcohol and water, the mixture will be more than 2
1
/
2
times as viscous (“thick”) as either the pure alcohol or the pure water. The reason is that alcohol molecules and water molecules attract and stick to one another by forming so-called hydrogen bonds. They cannot flow as freely as the less hindered molecules can in either pure alcohol or pure water. The properties of the mixture, including what it can and cannot dissolve, vary as the percentage of alcohol varies. If a given substance dissolves in pure alcohol or pure water, that doesn’t mean it will dissolve in any given mixture of alcohol and water.

Is all of this mere theory? No. I did an experiment to test it.

Annatto seeds, also known as
achiote
(ah-chee-OH-te), are the seeds of the tropical evergreen shrub
Bixa orellana
. They are coated with a paste-like oil containing an intense yellow-orange carotenoid pigment called bixin, which dissolves in oils and in alcohol but not in water. Annatto’s bixin is an FDA-approved coloring for fatty foods such as butter, margarine, and process cheeses. In this experiment, I used the highly visible bixin to simulate an alcohol-soluble flavor component in a food.

I placed five annatto seeds into each of four small test tubes and added 15 milliliters (a tablespoon) of one of the following liquids to each tube: water, a chardonnay containing 13 percent alcohol, a vodka containing 40 percent alcohol (80 proof), and 95-percent-pure ethyl alcohol. I let the tubes stand at room temperature for several days, shaking occasionally.

Here are the results: Neither the water nor the wine showed any dissolved bixin color at all; the water remained colorless and the white wine remained, well, white-wine colored. The vodka turned mildly yellow from a small amount of dissolved bixin, while the 95-percent-pure alcohol turned intensely yellow.

Conclusion: Wine—even straight, undiluted wine—doesn’t dissolve or “release” any alcohol-soluble bixin from the seeds. The alcohol concentration has to be high, some 40 percent or higher, to extract any appreciable amount of bixin. But such high alcohol concentrations never occur in cooking. Adding half a cup of vodka to a quart of sauce would produce a solution of only about 5 percent alcohol, even lower than the completely ineffective alcohol concentration in undiluted wine.

But that was at room temperature. What happens in the heat of cooking?

Although most substances are more soluble at higher temperatures, the facts of life regarding hydrogen bonding are still in effect. So while hot, pure alcohol will extract more alcohol-soluble components at higher temperatures, hot wine still won’t. So the “wine extracts flavors” theory still doesn’t hold water, so to speak.

Nevertheless, the alcohol in wine can contribute to flavor beyond the flavors inherent in the wine itself. During cooking, the alcohol can react chemically with acids in the food to form fragrant, fruity compounds called esters. You can demonstrate this by vigorously shaking some denatured ethyl alcohol (available in hardware and paint stores) with vinegar (acetic acid) in a tightly sealed bottle. After shaking for several minutes, open the bottle carefully and sniff; in addition to the odors of the alcohol and vinegar, you will detect a fruity note of ethyl acetate, one of the esters in the aroma of pineapple.

In the cooking pot, alcohol can react also with oxidizing substances to form aldehydes—compounds responsible for flavors such as almond, cinnamon and vanilla. Both the esters and the aldehydes are new flavors that were not present in the original ingredients. And contrary to widespread belief, the alcohol never “boils off” completely. It has plenty of time to take part in these chemical reactions during cooking.

So enjoy your
coq au vin
and
boeuf Bourguignonne
. The wine will add flavor in several ways, but don’t expect it to “extract” or “release” any alcohol-soluble flavors from your food.

And now that I think of it, why must we extract flavor compounds from our food, anyway? If they’re in there, they’re in there, and we’ll taste them when we chew, whether they are in the solids or the sauces.

I’m in the market for a backyard barbecue grill and I’m trying to decide between gas and charcoal. Everyone I ask has a different opinion—that is, one of two opinions, and they’re all fanatical about their choice. Do you have some objective advice?

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I
try not to get into politics or controversy in this book, but this issue is so critical, and the two candidates so contrasting, that I cannot resist asserting my position on this, the most contentiously debated concern of our time: “Which is better, charcoal or gas?” I hereby express my wholehearted endorsement of charcoal.

Caution: The opinions expressed below are inflammatory. Reader discretion is advised.

Grilling is hot these days. (Weak pun intended.) I have eleven grilling cookbooks on my bookshelves, but they all shrewdly gloss over two important points: that grilling and barbecuing are not the same thing, and that all fuels are not created equal.

Recognizing that almost no one understands the distinction between grilling and barbecuing, the cookbooks include both kinds of recipes in order to appeal to as many backyard Escoffiers as possible. And because an estimated 70 percent of all “barbecue grills” (a name that only compounds the confusion) in the United States are gas-fired, the authors stifle their unanimous but secret conviction (which they would admit only under oath) that charcoal is clearly superior to gas for grilling. An author cannot afford to lose a major segment of his or her potential readers, many of whom have shelled out big bucks for Brobdingnagian stainless steel, 18-wheeler gas grills equipped with everything but cruise control and a global positioning system.

In true grilling, the food is placed within several inches of a very hot—500 to 1000ºF (260 to 540ºC)—smoke-free fire and cooked quickly. Think of steaks, chops, hamburgers, kebabs, sausages, chicken parts, whole fish and shrimp, to name the most commonly grilled foods.

Barbecuing, on the other hand, consists of long (several hours), slow, relatively low-temperature cooking—300 to 350ºF (about 150 to 180ºC) or even lower—with the food confined in a pit or some sort of enclosure along with a (generally) smoky fire. Think of beef or pork ribs, pork shoulder, or brisket being slathered with top-secret sauces by men wearing cowboy hats. I’ll stick to grilling here.

There are three kinds of fuels: lump charcoal, briquettes, and gas.